Seal shaft shutoff device and method

ABSTRACT

An apparatus for providing a secondary seal on mixers and similar rotating equipment that includes a stop assembly and a collar which cooperate to minimize translational movement of a mixer shaft during shutoff and to form a reversible seal between the vessel and the shaft. The apparatus provides a sealing engagement between the mixing vessel and the rotatable shaft of a mixer offering improved safety during mechanical seal replacement.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for sealing amixing vessel. More particularly, the present invention relates to anapparatus for reversibly providing sealing engagement between a vesseland a shaft extending through a wall of the vessel. The invention isuseful, for example, for providing a temporary seal during replacementof a mechanical seal, which mechanical seal primarily provides sealingengagement between a mixing vessel and a rotatable shaft.

BACKGROUND OF THE INVENTION

In material processing equipment such as mixers, it is common that arotatable shaft is positioned through a wall of a mixing vessel. Thispenetration is commonly located at the centerline of the top head of themixing vessel, but may also occur in the sidewall or the bottom head. Ina typical mixer assembly, a mechanical seal is employed around therotatable shaft to close off the annulus surrounding the shaft where theshaft passes through the mixing vessel. These seals prevent the materialbeing agitated from escaping. In addition, the seals prevent any gasesthat may form during the agitation process from escaping.

A mechanical seal typically includes a stationary member fixed to theseal housing and a mating rotatable member attached to the mixer shaft.Seals are generally considered wearing components in a mixing system andmust be replaced relatively frequently. Large hydrostatic pressures thatcan be present inside the vessels and the replacement of mechanicalseals under elevated vessel pressure poses safety risks for maintenancepersonnel. Replacement of the mechanical seal without an additionalmeans of sealing the vessel can allow dangerous gases to escape and canalso allow the shaft to be thrust upwards if the vessel is pressurizedand no mechanical provision is in place to retain the mixer shaft.

As a result, replacing mechanical seals typically requiresdepressurization of the mixing vessel to eliminate the very largehydrostatic thrusts and the possibility of vapor release to theatmosphere present in the mixing vessel. The de-pressurization of themixing vessel can be undesirable for various reasons. First, the processfor reducing vessel pressure can be very time consuming. It takesconsiderable time to cool the vessel. There are also numerous safetyprocedures for locking out the mixer drive to prevent operation duringmaintenance. Proper ventilation of the vessel and elimination ofdangerous vapor levels is required before vessel entry is permitted.These can result in hours to days of delay depending on the installationspecifics. Eliminating downtime must be kept to a minimum because manytimes a mixer is critical to the operation of an entire plant and downtime represents lost production capacity. Second, certain applicationsrequire that the mixing vessel not be de-pressurized because it maycause the loss of valuable product or the manufacturing process mayrequire that the materials being agitated remain under constantpressure. The depressurization of the mixing vessel additionally posesenvironmental concerns, for example, the emissions escaping from themixing vessel may violate environmental guidelines and/or the contentsof the vessel may pose health risks to maintenance personnel.

Current methods for replacing seals without tank de-pressurizationattempt to create a temporary, secondary seal but involve partialdisassembly of the mixer and necessary shaft translation to engage theshutoff. In order to allow for shaft translation with the currentmethods, the bearings have to be disconnected from the shaft. The shafttranslation can be intentional as a result of operating the shutoffmechanism or it can be unintentional as a result of the hydrostaticpressure in the vessel acting on an unsupported shaft. Regardless, thetranslational movement poses safety hazards: gross movement upward ordownward can result in physical injury to maintenance personnel andbecause the mixer is at least partly disassembled, gases can escapeduring shaft translation, prior to formation of the secondary seal.Further, the translational movement imposes wear on secondary sealcomponents and also exposes those components to dirt and corrosiveelements. As a result of wear, dirt, and corrosion, if the shaft doesnot translate sufficiently to create an effective secondary seal, vaporscan escape.

For example, to replace cartridge seals, the mixer is disassembled andshaft translation is used during shutoff to create a secondary seal. Asa result, vapors can escape from the tank during the delay in formingthe seal while the shaft translates or as a result of incompletetranslation due to corrosion and dirt. Further, replacement of cartridgeseals typically use a common shaft support ring and shutoff collar whichonly provide for restrained downward movement and unrestrained upwardmovement. Such an arrangement does not incorporate a positive staticshaft seal, which can be checked for positive closure, and positivelocked support.

Accordingly, it is desirable to provide a method and apparatus foreffectuating a secondary seal which allows a vessel to remainpressurized during the mechanical seal replacement procedure, and whichminimizes fugitive emissions to the atmosphere. It is also desirable toprovide a method and apparatus for effectuating a secondary seal thatdoes not involve gross translational movement of the shaft or requirethe bearing support to be disconnected from the shaft for the shutoff tooperate. It is also desirable to have a means to safely confirm that theshutoff has occurred. It is also desirable to have an external means fordetermining that the shaft is properly supported in the shutoff mode. Itis further desirable to provide a method and apparatus for effectuatinga secondary seal that minimizes exposure of the secondary seal to wear,dirt, and corrosive elements.

SUMMARY OF THE INVENTION

The foregoing needs are met, at least in part, by the present inventionwhere, in one aspect, an apparatus is provided for use with a vesselhaving a shaft extending therethrough, wherein the apparatus has a stopassembly and a collar which cooperate to minimize translational movementof the shaft during shutoff and to form a reversible seal between thevessel and the shaft. In some embodiments a floating flushing bushingmay be incorporated with the apparatus to assist in keeping theapparatus clean.

In another aspect of the invention, a method is provided for minimizingshaft translation during shutoff and for creating a seal in the shutoffposition.

The above and other aspects, features and advantages are achievedthrough the use of novel seal shutoff assemblies as herein disclosed. Inaccordance with one embodiment of the invention, a seal shutoffapparatus is provided for use with a vessel having a shaft extendingtherethrough, wherein the seal shutoff apparatus includes a housinghaving an inner surface and an inward protrusion extending along theentire inner surface of the housing, a collar fixedly disposed on theshaft and protruding into the housing, a hydraulic nut mounted to thehousing and a moveable element connected to the hydraulic nut so thatthe moveable element is axially moveable at least between an operatingand shutoff position, wherein the moveable element contacts both thecollar and the inward protrusion to form a seal when the moveableelement is in the shutoff position.

In accordance with another embodiment of the present invention, the sealshutoff apparatus includes a housing having an inner surface and aninward protrusion extending along the entire inner surface of thehousing; a collar fixedly disposed on the shaft and protruding into thehousing; a first hydraulic nut mounted to the housing; a secondhydraulic nut mounted to the housing; a first moveable element connectedto the first hydraulic nut for axial movement at least between anoperating position and a shutoff position, wherein the first moveableelement is located to one side of the collar and inward protrusion; anda second moveable element connected to the second hydraulic nut foraxial movement at least between an operating position and a shutoffposition, but located on the opposing side of the collar and inwardprotrusion, wherein the moveable elements contact both the collar andthe inward protrusion to form a seal when the moveable elements are inthe shutoff position.

In accordance with yet another embodiment of the invention, a method forforming a reversible seal is provided, wherein the hydraulic nut(s)is(are) actuated to move the shutoff disc from an operating to a shutoffposition, resulting in the shutoff disc contacting both the collar andinward protrusion to form a seal.

In yet another embodiment of the present invention, a seal shutoffapparatus for use with a vessel having a shaft extending therethrough,wherein the shaft translates at least between an operating position anda shutoff position, is provided. The seal shutoff apparatus has a stopmechanism and a shaft shutoff collar that cooperate both to constraintranslational movement of the shaft and to form a seal between thevessel and the shaft when the shaft is in the shutoff position.

In accordance with yet a further embodiment of the invention, a methodof forming a reversible seal is provided, wherein the shaft shutoffcollar is moved to the shutoff position causing the collar to contactthe stop mechanism thereby creating a seal.

There has thus been outlined, rather broadly, several features of theinvention in order that the detailed description thereof that followsmay be better understood, and in order that the present contribution tothe art may be better appreciated. There are, of course, additionalfeatures of the invention that will be described below and which willform the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract, are for the purpose ofdescription and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a seal shaft shutoffapparatus in the operating position in accordance with an embodiment ofthe present invention.

FIG. 2 is a partial cross-sectional view of the apparatus of FIG. 1 inthe shutoff position.

FIG. 3 is an exploded cross-sectional view of a floating flushingbushing which can be used in combination with embodiments of the presentinvention.

FIG. 4 is a partial cross-sectional view of a seal shaft shutoffapparatus in the operating position in accordance with anotherembodiment of the present invention.

FIG. 5 is a partial cross-sectional view of the apparatus in FIG. 4 inthe shutoff position.

FIG. 6 is a side view of a mixer employing a mixer seal shaft shutoffapparatus in accordance with the present invention.

FIG. 7 is a partial cross-sectional view of a seal shaft shutoffapparatus in the operating position in accordance with anotherembodiment of the present invention.

FIG. 8 is a partial cross-sectional view of the apparatus in FIG. 7 inthe shutoff position.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides an apparatus for forming a reversibleseal to minimize the escape of fugitive emissions through the annulussurrounding a shaft passing through a vessel. By “reversible seal,” itis understood that the apparatus has an operating position in which aseal is not formed and a shutoff position in which a seal is formed. Theapparatus is preferably used in conjunction with a primary, mechanicalseal and is suitable for providing a secondary seal during replacementof the primary, mechanical seal. In such an arrangement, the apparatusis typically in the operating position except when the primary,mechanical seal is being replaced in which case the apparatus is in theshutoff position. In the embodiments depicted, the shutoff assembliesare utilized in combination with an industrial mixer and are shown in avertical axis typical of top entering mixers. It should be understood,however, that the present invention is not limited in its use to topentering mixers but can be used, for example, with bottom entering orside entering mixers. Furthermore, the present invention is not limitedin its application to industrial mixers, but, for example, can be usedwith other devices having shafts such as pumps, centrifuges, marineapplications such as line shafting penetrations in the hull, etc.

Referring now to the figures, wherein like reference numerals indicatelike elements, FIGS. 1 and 2 show a partial cross-sectional view of aseal shaft shutoff apparatus 10, in accordance with an embodiment of theinvention, disposed on a rotatable shaft 12. Whereas FIG. 1 depicts theapparatus 10 in an operating position, FIG. 2 depicts the apparatus 10in a shutoff position.

As shown in FIGS. 1 and 2, the apparatus 10 includes a housing 14 havingan inner surface 16 and an inward protrusion 18, a collar 20 fixedlydisposed on the shaft 12 and protruding into the housing 14, and stopassembly 22 having moveable elements 24, 26 actuated by hydraulic nuts28, 30 between an operating position (FIG. 1) in which the moveableelements 24, 26 are spaced apart from the collar 20 and the inwardprotrusion 18 and a shutoff position (FIG. 2) in which the moveableelements 24, 26 sealingly engage both the collar 20 and the inwardprotrusion 18 simultaneously.

As depicted, the housing 14, which can be a single unit, includes alower housing 32, a middle housing 34, and an upper housing 36, inaddition to the inward protrusion 18. The tri-part structure is for easeof assembly and disassembly. Specifically, the lower housing 32 isdetachable from the middle housing 34 for assembly purposes and thelower 32 and middle 34 housings are in turn supported by the upperhousing 36 via a bolt 37 or other suitable affixing means known in theart. The upper housing 36 is firmly attached to the mixer at the mixermounting flange (not shown). Alternatively, the upper housing 36 can bean integral part of the mixer mounting flange. The mixer mounting flangeprovides a seal between the vessel and housing 14 which alleviates orprevents loss of pressure and/or vapors.

The housing 14, including the lower 32, middle 34, and upper 36 housingsare preferably provided by any material suitable for applications wherethe mixing conditions are conducted under extreme temperatures and/orthe materials to be mixed are corrosive. More preferably those materialsare wetted metals such as 316 stainless steel and/or titanium.

The inward protrusion 18 extends toward the collar 20 along the entireperimeter of the inner surface 16 of the housing 14. The length of theinner protrusion 18 varies and depends on the width of the housing 14,the distance the collar 20 extends from the shaft 12, and the width ofthe moveable elements 24, 26. The length of the inner protrusion 18,however, is preferably such that it does not contact the collar20—allowing the shaft 12 and collar 20 to rotate without providing anywear on the inward protrusion 18—but does overlap the moveable elements24, 26 as shown in the figures. More preferably, the length is such thateven operating shaft runout will not cause contact between the shaft 12and inward protrusion 18.

The inward protrusion is also preferably provided by any materialsuitable for applications where the mixing conditions are conductedunder extreme temperatures and/or the materials to be mixed arecorrosive, for example, wetted metals such as 316 stainless steel and/ortitanium. The width of the inner protrusion 18 depends in part on thetype of material chosen. The width is preferably such that the givenmaterial will not be damaged when squeezed by the pressure exerted bythe moveable elements 24, 26.

The collar 20, as the name suggests, encircles the entire circumferenceof the shaft 12. The collar 20 may be integral with the shaft 12, may beattached by welded fabrication, or may be attached by any means known inthe art, such as with set screws and sealed with o-rings. An integral orwelded arrangement is generally preferred. However, other attachingmeans, such as the set screw/o-ring arrangement, can be employed. Thelength of the collar 20 (i.e. the distance the collar 20 extends intothe housing) can vary and depends in part on the length of the moveableelements 24, 26. The collar 20 should be long enough such that itextends between moveable elements 24, 26 and such that, when moveableelements 24, 26 are in the shutoff position, the shaft 12 can besupported. The collar 20, too, is provided by any material suitable forapplications where the mixing conditions are conducted under extremetemperatures and/or the materials to be mixed are corrosive, forexample, wetted metals such as 316 stainless steel and/or titanium. Thewidth (i.e. the thickness) of the collar 20 depends in part on thematerial chosen. The width is preferably such that the given materialwill not be damaged when squeezed by the pressure exerted by themoveable elements 24, 26 in the shutoff position.

As depicted, the stop assembly 22 includes first and second moveableelements 24 and 26 actuated by first and second hydraulic nuts 28 and 30respectively. The stop assembly 20 can optionally include additionalhydraulic nuts and/or biasing means 38 for preventing engagement, suchas the illustrated Belleville spring washers.

The first and second moveable elements 24 and 26 are preferablyring-shaped, i.e. have an interior and exterior diameter, but can be anyshape as long as they encompass the entire circumference of the shaft 12and span the gap between the collar 20 and the inward protrusion 18. Themoveable elements 24, 26 are preferably sized such that the surface 40of the interior diameter does not contact the shaft, and such that thedistance between the interior diameter and exterior diameter is largeenough to span the gap between the collar 20 and the inward protrusion18. The interior diameter is preferably large enough so that themoveable elements 24, 26 do not contact the shaft 12 even due toaccidental lateral (i.e., perpendicular to the shaft centerline)movement of the shaft 12.

While the illustrated embodiment depicts two moveable elements 24, 26flanking the collar 20 and inward protrusion 18, alternative embodimentsand/or modifications having only a single moveable element also fallwithin the scope of the invention. For example, apparatuses employed onmixing assemblies where it is expected there will be a downward thrustexerted on the shaft only, can operate safely and effectively utilizinga single lower moveable element. Similarly, apparatuses employed onmixing assemblies where it is expected that the shaft will onlyexperience an upward thrust, can be configured with an upper moveableelement only and operate safely and effectively. Though embodimentsutilizing only a single moveable element are described, the utilizationof two moveable elements is preferred from a safety standpoint.

The moveable elements 24, 26 are preferably provided by any materialsuitable for applications where the mixing conditions are conductedunder extreme temperatures and/or the materials to be mixed arecorrosive, for example, wetted metals such as 316 stainless steel and/ortitanium.

The hydraulic nuts 28, 30 are commercially available. Alternatively,where the commercial products are not appropriate from, for example, ageometry or materials stand point, designs specifically can be made.Custom designed hydraulic nuts are appropriate and preferred forexample, for applications where the materials to be mixed are corrosiveand can attack the hydraulic nut surfaces. Therefore, corrosiveresistant wetted metals such as 316 stainless steel and/or titanium arepreferred. In addition, custom geometries can be appropriate where thehousing 14 dimensions require that the outer diameter (OD) and/or theinner diameter (ID) of the hydraulic nut be different than that ofstandard, commercially available hydraulic nuts.

The apparatus 10 can optionally include additional sealing elements 41,42, 43, 44, 45, 46. Sealing elements 43, 44 are preferably disposed onthe surface 27 of moveable element 26 facing the collar 20 and inwardprotrusion 18, and are in a spaced apart position such that sealingelement 43 engages the collar 20 and sealing element 44 engages theinward protrusion 18 when the moveable element 26 is in the shutoffposition. Sealing element 41 is disposed on the surface 21 of the collar20 facing moveable element 24, and is positioned such that it engagesthe moveable element 24 when the moveable element 24 is in the shutoffposition. Sealing element 42 is disposed on the surface 19 of inwardprotrusion 18 facing moveable element 24 and is positioned so that itengages moveable element 24 when the moveable element 24 is in theshutoff position. Sealing elements 45 and 46 seal the upper, middle, andlower housings to each other.

The illustrated placement of the sealing elements 41, 42, 43, 44 offersease in manufacture of the sealing apparatus and, in addition, allowsgravity to assist in keeping the sealing elements 41, 42, 43, 44 inposition. The sealing elements 41, 42, 43, 44, are preferably O-ringtype seals but other means known in the art, including graphite packingand plastic type sealing elements such as TEFLON® vee rings, can beused.

FIGS. 1 and 2 together illustrate operation of the seal shutoffapparatus. As shown in FIG. 1, when the mixer is in use and the shaft isrotating, moveable elements 24, 26 are in the operating position. Byoperating position, it is understood that the moveable elements 24, 26are spaced apart from the collar 20 and the inward protrusion 18 so thatthe shaft 12 can rotate. Preferably, moveable elements 24, 26 do notcontact the collar 20 and inward protrusion 18. More preferably, thedistance between the surfaces 25, 27 of the moveable elements 24, 26 andthe surfaces of the collar 21, 23 and surfaces of the inward protrusion17, 19 is minimized to limit accidental translational movement of theshaft 12 but large enough so that any runout of the shaft 12 duringrotation does not result in accidental contact between collar 20 and themoveable elements 24, 26 resulting in undesirable wear of thosecomponents. For industrial mixers having shafts ranging in diameter fromabout 2″ to about 20″, the preferred distance ranges from about 0.06″ toabout 0.19″, more preferably ranges from about 0.09″ to about 0.15″, andis even more preferably about 0.125″. Further, the Belleville washers 38assist in preventing or alleviating the moveable elements 24, 26 fromengaging and contacting the collar during operation of the mixer andwhile the shaft 12 is rotating during mixer operation.

As shown in FIG. 2, when the mixer is shutoff and the shaft 12 stopsrotating, the moveable elements 24, 26 are actuated from the operatingposition to the shutoff position by hydraulic nuts 28, 30. By shutoffposition it is understood that the mixer is not in use, the shaft 12 isno longer rotating, and the moveable elements 24, 26 engage the collar20 and inward protrusion 18. The moveable elements 24, 26 are axiallydisplaced by the pressurization of the hydraulic nuts 28, 30 such thatthe inner surfaces 25, 27 of the moveable elements are in contact withthe first surface 21 and second surface 23 of the collar 20 and thefirst surface 19 and second surface 17 of the inward protrusion 18. Thefirst surfaces of the collar 20 and inward protrusion 18, 21 and 19respectively, face the inner surface 25 of the moveable element 24. Thesecond surfaces of the collar 20 and the inward protrusion 18, 23 and 17respectively, face the inner surface 27 of the moveable element 26.Preferably, the inner surfaces 25 and 27 are in sealing engagement withthe respective surfaces of the inner protrusion 17, 19 and the collar21, 23, form a secondary seal in addition to the mixer's mechanicalseal.

External pressurization of the hydraulic nuts 28, 30 results in an axialreaction force on the internal piston of the hydraulic nuts 28, 30actuating both of the moveable elements 24, 26 until the moveableelements 28, 30 sealingly engage the collar 20 and the inward protrusion18, thereby providing a reversible, secondary seal between the mixervessel (not shown) and the shaft 20.

External pressurization to actuate the apparatus 10 allows forcontinuous monitoring of the apparatus 10 during initial shutoff at asafe distance from the vessel. By the closure of an isolation valvebetween the external pressurization source and the apparatus 10 anyobserved loss of pressure indicates a failure in the hydraulic nutassemblies 28, 30 and therefore a failure in forming the secondary seal,signaling that appropriate action should be taken—for example,depressurizing the mixing vessel—before changing the mixer seal to avoidor alleviate safety hazards. Both the ability to remotely observepotential problems and to take remedial action decrease the likelihoodof maintenance personnel coming into contact with the contents of themixing vessel or being harmed by an unanticipated seal shafttranslation.

In addition, the previously described actuation process allows the mixerto remain assembled during the shutoff procedure, minimizing andpreferably preventing, maintenance personnel from encounteringunanticipated shaft translations during shutoff. Maintaining theintegrity of the mixer also allows the tank to remain pressurized and/orclosed during the shutoff procedure alleviating and preferablypreventing loss of tank pressure and/or escape of harmful vapors.

The present invention contains additional safety features that work bothseparately and in combination with previously described features. Forexample, as described above, the moveable elements 24, 26 are preferablyspaced apart to minimize unintentional shaft translation to alleviate oravoid physical harm to equipment operators.

Specifically, should there be a loss of hydraulic pressure to thehydraulic nuts 28, 30 together with a net up thrust due to hydrostaticpressure in the mixer being greater than atmospheric pressure, the shaft12 can be unintentionally displaced upward. However, because translationof the shaft 12 will cause the collar 20 to contact moveable element 24,in turn resulting in translation of moveable element 24 and compressionof the piston in hydraulic nut 28 until the stroke of the piston isexhausted, unintentional shaft translation can be minimized.Specifically, the shaft 12 will only translate as far as the combinationof the distance between the surface 21 of the collar 20 and the surface25 of the moveable element 24 and the distance the piston compresses.For an industrial mixer having an approximate shaft diameter within therange of 2.0″-20.0″, shaft translation is preferably limited to a rangeof from about 0.06″ to about 0.19″, is more preferably limited to arange of from about 0.09″ to about 0.15″, and is even more preferablylimited to about 0.125″. As an additional benefit, close clearancebetween the parts can minimize the loss of tank pressure and vaporemission.

Similarly, should there be a loss of hydraulic pressure to the hydraulicnuts 28, 30 and a resulting net downward thrust on the shaft 12,downward movement of the shaft 12 will be constrained by the collar 20contacting moveable element 26 which in turn compresses the piston inhydraulic nut 30 until it rests against the lower housing 32. For thesame industrial mixer described in the previous paragraph, shafttranslation is again preferably limited to a range of from about 0.06″to about 0.19″, and is more preferably limited to a range of from about0.09″ to about 0.15″, and is even more preferably limited to about0.125″.

An optional pressure tap 47, shown in FIGS. 1 and 2 provides yet anadditional failsafe mechanism. The optional pressure tap 47, located inthe upper housing 36, allows maintenance personnel to monitor theperformance of the shutoff after it is engaged to make certain that allsealing elements are functioning properly and that it is safe to proceedwith the mechanical seal replacement. Any increase in pressure sensed atthe pressure tap 47 would indicate that the shutoff apparatus 10 is notfunctioning correctly. This pressure tap is also used to initiallyrelieve captured pressure between the shutoff apparatus and themechanical seal.

The pressure tap 47 employs a release valve and pressure gauge, both ofwhich are integral to the pressure tap structure. The pressure tap 47works by first activating the shutoff assembly 10. After the assembly 10is activated, the release valve of the pressure cap may be opened,releasing gas pressure trapped within the assembly 10. Initially the gaspressure released may be significant, but it should subsidesubstantially to that of the ambient atmospheric pressure. Thisoccurrence indicates that the sealing elements 41, 42, 43, 44 andmoveable elements 24, 26 are functioning properly and the mechanicalseal may be removed safely. However, if a condition occurs where the gasrelease remains constant and fails to subside, this is indicative of thesealing elements and moveable elements failing to function properly,alerting maintenance personnel that the mechanical seal can not beremoved safely.

FIG. 3 illustrates a standard floating flushing bushing 48, which ispreferably positioned in close clearance to the shaft 12. Preferably,the bushing is positioned in a range of from about 0.001″ to about0.003″ from the shaft. The bushing 48 is also preferably operationallyconnected to the apparatus so that it deflects radially with themovement of the shaft 12 to prevent wear.

The bushing 48 can also function to keep the assembly 10 and the mixerseal clean during mixer operation, which can help maintain propersealing of the apparatus 10 over time. Cleanliness is maintained both bythe bushing 48 being positioned in close clearance to the shaft 12, thusalleviating the problem of dirt and corrosive elements contacting thesealing elements, and also by being used cooperatively with a flushingvent 49, which vent 49 delivers liquid to the spaces surrounding thebushing 48, including between the bushing 48 and shaft 49. Preferably,the standard floating flushing bushing 48 is used in combination thewith seal shaft shutoff apparatus, however the bushing is not requiredfor the apparatus to function properly.

Referring now to FIGS. 4 and 5, a partial cross-sectional view of a sealshaft shutoff apparatus 100, disposed around a rotatable shaft 105, isshown in accordance with an alternative embodiment of the presentinvention. Whereas FIG. 4 depicts the apparatus 100 in an operatingposition. FIG. 5 depicts the apparatus 100 in a shutoff position.

As shown in FIGS. 4 and 5, the apparatus 100 includes a stop assembly101 having first contact surface 102 spaced apart from a second contactsurface 103, a collar 104 fixedly disposed on a shaft 105, and a sealingmechanism 106.

The stop assembly 101 can be a single unit. As depicted, however, thestop assembly 101 comprises a first component 107 including the firstcontact surface 102, attached to a second component 109 including thesecond contact surface 103. The first and second components 107, 109 canbe attached together by any means known in the art, for example by abolt 110.

The stop assembly 101, which is sealingly mounted to the vessel 111,extends inward, toward the shaft 105, along the entire perimeter of thevessel 111. In the embodiment shown, the sealing engagement isaccomplished by having the mechanical seal mounting flange 112 alsofunction as the first component 107 having the first contact surface102. In other words, in the illustrated embodiment, the first contactsurface 102 is integral with the mechanical seal mounting flange 112.

The collar 104 encircles the entire circumference of the shaft 105.Preferably, it is integral with the shaft 105, however the collar 104may be attached by welded fabrication, set screws or any other meansknown in the art.

The collar 104 is provided by any material, for example, wetted metalssuch as 316 stainless steel and/or titanium, suitable for extremetemperature mixing applications and/applications where the materials tobe mixed are corrosive and can attack the collar 104.

The sealing mechanism 106 can be a separate mechanism, or as depicted,can be integral with the stop assembly 101 and collar 104. In theintegral arrangement shown, the sealing mechanism 106 includes firstnotched surface 113, which can be considered a portion of the firstcontact surface 102, second notched surface 114, and optional sealingelement elements 115, 116. Optional sealing elements 115, 116 arepreferably positioned on second notched surface 114, thus allowinggravity to assist in keeping the sealing elements 115, 116 in position;and such that when the collar 104 is in shutoff position, sealingelements 115, 116 engage the first notched surface 113. Sealing elements115, 116 are preferably o-ring type seals but other means known in theart, including graphite packing and plastic-type sealing elements suchas TEFLON® vee rings may be used.

It should be noted that the position of the sealing mechanism 106 andarrangement of notched surfaces 113, 114 and sealing elements 115, 116shown is that preferred for top entering mixers for which upward shafttranslation is expected. Thus, for example, for top entering mixers inwhich downward shaft translation is expected, the sealing mechanism 106would preferably be located below or integral with the second contactsurface 103.

It should also be noted that alternative integral assemblies are alsowithin the scope of the invention. For example, an integral sealingassembly could merely include the flat portion of first contact surface102, a surface 120 of the collar 104 opposing the flat portion of firstcontact surface 102, and at least one optional, additional sealingelement (not shown) such as an o-ring disposed on flat portion ofsurface 120.

The seal shaft shutoff assembly 100 optionally includes a floatingflushing bushing 121 and flushing vent 122. As discussed above, FIG. 3illustrates a standard floating flushing bushing. The bushing 121,particularly in conjunction with the flushing vent 122, functions tokeep the stop assembly 101 clean during mixer operation by alleviatingor preventing dirt and corrosive elements from coming in contact withthe sealing elements and opposing surfaces of the collar and stopassembly.

Again, as in the previously described embodiment, the bushing 121 isspaced apart from the shaft and preferably operationally connected tothe assembly 101 so that it deflects radially with the movement of theshaft 105 to maintain a spaced apart position relative to the shaftthereby preventing or alleviating wear. For example, the bushing 121 canbe connected to the stop assembly 101 by the bolt 110. Also as discussedabove, the bushing is also positioned in close clearance from the shaft105, in a range of from about 0.001″ to about 0.003″ from the shaft 105.

Preferably, the floating flushing bushing is used in combination thewith seal shaft shutoff apparatus, however the bushing is not requiredfor the apparatus to function properly.

FIGS. 4 and 5 together illustrate operation of the seal shutoffapparatus 100. As shown in FIG. 4, when the mixer is in use and theshaft 105 is rotating, the collar 104 is in operating position. Byoperating position, it is understood that the collar 104 is spaced apartfrom the stop assembly 101. Preferably, the distance between the collar104 and the stop assembly 101 is minimized to limit translation of theshaft 105 but large enough so that wobbling of the shaft 105 duringrotation does not result in accidental contact between the collar 104and the stop assembly 101. For industrial mixers with shaft diametersbetween 2.0″-20.0″, this distance preferably ranges from about 0.06″ toabout 0.19″. More preferably the distance ranges from about 0.09″ toabout 0.15″. Even more preferably, the distance is about 0.125″.

As shown in FIG. 5, when the mixer is shutoff, the shaft 105 translates,displacing the collar 104 from the operating position to the shutoffposition. Shaft translation can be, in the case of a top entering mixer,either upward or downward resulting from a pulling or pushing forceexerted by an external device (not shown), upward as a result ofhydrostatic pressure in the mixer, or downward as a result of gravity.It should be noted that when an external device is used, preferablyhydrostatic pressure assists in raising the shaft into an upward shutoffposition, or gravity assists in lowering the shaft into a downwardshutoff position. By shutoff position, it is understood that the collar104 engages either the first contact surface 102 as in the case ofupward translation, or the second contact surface 103, as in the case ofdownward translation, and the sealing mechanism is engaged.

Accordingly, as shown in FIGS. 4 and 5, the stop assembly 101 cooperateswith the collar 104 to minimize shaft translational movement—bothintentional and unintentional. For industrial mixers having shaftdiameters between 2.0″-20.0″, this distance preferably ranges from about0.19″ to about 0.38″. More preferably the distance ranges from about0.20″ to about 0.27″. Even more preferably, the distance is about 0.25″.

Referring now to FIG. 6, a mixer 200 employing a seal shaft shutoffapparatus 10 in accordance with the present invention is illustrated.The mixer 200 includes a rotatable shaft 202 that extends from a drivingmeans 204 such as a motor driven geardrive. The shaft 202 proceeds topass through the mixer seal 206 and onto the shutoff assembly 10, whereit extends through the assembly 10 and eventually penetrates the mixingvessel 208. A puller assembly 203 is used to move the shaft 202 up anddown as necessary during the seal cartridge replacement. A mixermounting flange 201 supports the mixer and the shutoff apparatus 10while sealing the vessel 208 to the outside. The mixer mounting flangeis not disturbed or removed in any way during the replacement of theseal cartridge 206. It also contains the pressure connections for thepressure tap 47 and the hydraulic nut pressure ports 50.

Referring now to FIGS. 7 and 8, a partial cross-sectional view of a sealshaft shutoff apparatus 10, disposed around a rotatable shaft 12, isshown in accordance with an alternative embodiment of the presentinvention. Whereas FIG. 7 depicts the apparatus in the operatingposition, FIG. 8 depicts the apparatus 10 in the shutoff position.Unlike the previously described embodiments, FIGS. 7 and 8 illustrate analternative sealing element 41, 42, 43, 44 arrangement. As illustrated,the collar 20 has an upper shoulder and a lower shoulder. Both shouldershave a groove 62 and 64 within which sealing elements 41 and 43 aredisposed. In addition, sealing elements 43 and 44 are disposed withingrooves 66 and 68 of moveable elements 24 and 26 such that sealingelement 42 contacts the upper housing 36 of the apparatus and sealingelement 44 contacts the lower housing 32 of the apparatus. Thisarrangement may preferably be utilized where gravity is incapable or isnot expected to assist in keeping the sealing elements in position.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention. For example, while theillustrated embodiments are discussed in the context of providing a sealaround the annulus of a shaft, a person of ordinary skill shouldrecognize that the assembly can be configured to provide a seal in othercontexts.

As another example, a person of ordinary skill should recognize that theassembly can be used simply to support a shaft in shutoff position. Forsuch a use, the collar may not extend the entire circumference of theshaft, the inward protrusion may extend only partially along thecircumference of the inner surface of the housing, may be comprised ofseveral intermittent inward protrusions or may be eliminated altogether,and the stop assembly may only engage and need not sealingly engage thecollar and/or inward protrusion if present.

As yet another example, while FIGS. 1 and 2 indicate that the collar 20and inward protrusion 18 are positioned in the same plane andperpendicular to both the shaft 12 and housing 14, collar 20 and inwardprotrusion 18 may in fact be in separate planes and in non-parallelarrangement. In such a configuration, moveable elements 24, 26 would beshaped so that in shutoff position they would preferably be in sealingengagement with both the collar 20 and inward protrusion 18.

What is claimed is:
 1. A seal shutoff apparatus for use with a vesselhaving a shaft extending through the vessel, wherein the shafttranslates at least between an operating position and a shutoffposition, the apparatus comprising: a housing comprising an innersurface and an inner protrusion that extends along said inner surface ofsaid housing; a collar connected to the shaft such that the collartranslates with the shaft; a stop assembly comprising a first and asecond contact surface, wherein the first and second contact surfacesconstrain translational movement of the collar; and a sealing mechanism,wherein said collar extends between said first contact surface and saidsecond contact surface to generally oppose said inner protrusion.
 2. Anapparatus according to claim 1, wherein the sealing mechanism isintegral with the stop assembly, such that the first contact surfacetogether with the collar form a seal when the shaft is in the shutoffposition.
 3. An apparatus according to claim 1, wherein the stopassembly comprises a first component attached to a second component, thefirst component comprises the first contact surface and the secondcomponent comprises the second contact surface.
 4. An apparatusaccording to claim 1, wherein the sealing mechanism further comprisesO-rings.
 5. An apparatus according to claim 1, wherein the apparatusfurther comprises a floating flushing bushing and flushing vent, thebushing being operatively connected to the apparatus for tracking radialshaft deflection and being positioned a distance from the shaft rangingfrom about 0.001″ to about 0.003″.
 6. An apparatus according to claim 1,wherein the stop assembly constrains the collar from translating greaterthan about 0.19″ in a first direction and from translating greater thanabout 0.19″ in a second direction.
 7. An apparatus according to claim 6,wherein the stop assembly constrains the collar from translating greaterthan about 0.125″ in a first direction and from translating greater thanabout 0.125″ in a second direction.
 8. An apparatus according to claim7, wherein the first direction is upward and wherein the seconddirection is downward.
 9. A mixing apparatus for mixing and processingmaterials comprising: a mixing vessel configured for receiving materialto be mixed; a motor; a rotatable shaft extending from the motor andinto the mixing vessel; a sealing element for providing a primarysealing engagement between the vessel and the rotatable shaft; and anapparatus for providing secondary sealing engagement between the vesseland the rotatable shaft wherein the shaft translates at least between anoperating position and a shutoff position, the apparatus comprising ahousing comprising an inner surface and an inner protrusion that extendsalong said inner surface of said housing, a collar connected to theshaft such that the collar translates with the shaft; a stop assemblycomprising a first and a second contact surface, wherein the first andsecond contact surfaces constrain translational movement of the collar;and a sealing mechanism, wherein said collar extends between said firstcontact surface and said second contact surface to generally oppose saidinner protrusion.
 10. An apparatus according to claim 9, wherein thesealing mechanism is integral with stop assembly, such that the firstcontact surface together with the collar form a seal when the shaft isin the shutoff position.
 11. An apparatus according to claim 10, whereinthe sealing mechanism further comprises O-rings.
 12. An apparatusaccording to claim 9, wherein the stop assembly comprises a firstcomponent attached to a second component, the first component comprisesthe first contact surface and the second component comprises the secondcontact surface.
 13. An apparatus according to claim 9, wherein theapparatus further comprises a floating flushing bushing and flushingvent, the bushing being operatively connected to the apparatus fortracking radial shaft deflection and being positioned a distance fromthe shaft ranging from about 0.001″ to about 0.003″.
 14. An apparatusaccording to claim 9, wherein the stop assembly constrains the collarfrom translating in a first direction greater than about ⅛″ and fromtranslating in a second direction greater than about ⅛″.
 15. Anapparatus according to claim 14, wherein the first direction is upwardand wherein the second direction is downward.
 16. A method for providinga sealing engagement between a vessel and a rotatable shaft comprising:providing a seal shutoff apparatus having a housing comprising an innersurface and an inner protrusion that extends along said inner surface ofsaid housing, a collar connected to the shaft such that the collartranslates with the shaft, a stop assembly comprising a first and asecond contact surface, wherein the first and second contact surfacesconstrain translational movement of the collar, and a sealing mechanism,wherein said collar extends between said first contact surface and saidsecond contact surface to generally oppose said inner protrusion; andtranslating the collar in a first direction such that the first contactsurface together with the collar form a seal.
 17. A method according toclaim 16, wherein the first direction is upward.
 18. A method accordingto claim 16, wherein the first direction is downward.
 19. An apparatusfor use with a vessel having a housing and a shaft extending through thevessel, wherein the shaft translates at least between an operatingposition and a shutoff position, the apparatus comprising: an innerprotrusion that extends from the housing a first stopping meansconnected to the shaft such that the first stopping means translateswith the shaft; and a second stopping means disposed within theapparatus housing wherein the first stopping means together with thesecond stopping means constrain translational movement of the shaft to arange of from about 0.06″ to about 0.19,″ wherein said first stoppingmeans extends from the shaft to generally oppose the inner protrusion.20. An apparatus according to claim 19, wherein the first stopping meanssealingly engages the second stopping means when the shaft is in theshutoff position.